1. Field of the Invention
The present invention relates to the so-called TTL direct light measuring system for a single lens reflex camera for measuring the light reflected upon the film plane and the leading shutter curtain, whereby the light measuring range can be changed over by an electrical means.
2. Description of the Prior Art
The TTL direct light measuring system for the single lens reflex camera for measuring the light reflected upon the film plane and the leading shutter curtain has many merits. The real time light measurement of the object image during the exposure is possible, automatic exposure photography is possible when the lens aperture is closed, and TTL-flash light photography is possible. However, it is rather difficult to change the light measuring range between the average light measurement and the partial light measurement.
A device for changing over the light measuring range is already known. One light sensing element is arranged at the side of the bottom of the camera body. In front of the light sensing element two different optic systems for changing over the average light measuring range and the partial light measuring range are arranged to change the light measuring range. For example, the Japanese patent application Laid-Open No. Sho 53-98821 discloses a system that is shown in FIG. 1. The amount of light passing the photographing lens 1 and the half permeable plane in the quick return mirror 2 and reading the leading shutter curtain 3 and the film plane 4 is measured by means of a light sensing element 5 via optics. However, the changeover between the average light measuring range and the partial light measuring range is carried out by replacing the optics 6 with optics 7 making it necessary to provide a means for mechanically operating the two optics 6 and 7 from outside the camera resulting in a larger operating member and making quick operation difficult.